Terpene production in Solidago altissima in response to aphid herbivory José Garrido and Ray S Williams Appalachian State University

How Aphids Choose Plants ● Aphids may choose plants through architectural, chemical, or genetic ques. ○Increases in aphid distribution in Solidago is indirectly influenced by suits of herbivores that induce branching (Pilson 1992). ○In Populus angustiflora aphid herbivory often correlate positively with lower phenol levels (Zucker 1982). ● How aphids choose their individual host, as well as how exactly plants defend themselves from herbivory, is poorly understood.

Terpene Defenses ● Major plant defensive chemicals are alkaloids, phenolics, and terpenes. ● Terpenes, the largest group and can be induced by herbivory (Langenheim 1994). ○Plants can recognize and respond accordingly to herbivory and abiotic physical distress (Kempel et al. 2011). ○Responsive protection is cheaper than constantly elevated terpene levels.

Uroleucon nigrotuberculatum Red goldenrod aphid Solidago altissima Tall Goldenrod alt/Solidago_juncea_plant.jpg QNR701RMQDRIQJRQQNRQQR0U0DR7Q00P0R0MQTRIQH0U0FQ80BRX0FQ.jpg Uroleucon nigrotuberculatum

● Previous studies in the Williams’ laboratory at Appalachian State University have investigated the importance of terpenes in the choice of genotypes in Solidago by the specialist aphid Uroleucon nigrotuberculatum, including: Colonization of S. altissima collected from different habitats (Williams and Avakian 2015) Abundance on genotypes previously fed upon by a herbivorous beetle (Howells maters thesis) Abundance on different genotypes in different species of Solidago (Linquist capstone research) Effects of nutrient treatments and genotypes (Bonville masters thesis) What is still unknown is the effect of aphid feeding on terpene production in S. altissima

Our study addressed three questions: -How does aphid feeding affect terpene production in Solidago altissima? -Does aphid abundance differ among treatments and genotypes? -Is aphid abundance related to terpenes in leaves in support of prior research in the Williams lab? Questions Addressed

Methods Four plants in 5 genotypes were propagated and divided into 2 treatments: ○Treated with Marathon ○Untreated Plants were spatially separated Aphid abundance was recorded weekly Leaves for terpene analysis were collected at peak aphid abundance in September

● Gas chromatography protocol followed Williams and Avakian (2015) with ID using analytical standards ● ~2 grams of leaf material ground in 15 mL pentane ● Pentane is filtered and reduced to 0.5 mL using N 2 ● 1 µL injected into Shimadzu 14A GC ● Ten terpenes identified for comparisons among treatments

Terpene ID Example  α-pinene  β-elemene  germacrene-D  γ-elemene  ledene oxide (II)

Statistical Analyses Two-way ANONVA (Proc GLM, SAS) analyzed effects of treatment, genotype and their interaction Proportion of each terpene allocated among genotypes assessed Linear and Partial Least Squares Regression (PLS) used to relate terpenes to aphid abundance PLS Creates latent variables explaining the best fit and creates a prediction value Regression of observed vs. predicted provides correlation between terpenes and aphid abundance Highly effective with co-linear data

Results

Terpenes

Terpene Allocation

Summary Aphid abundance, as expected, was affected by the Marathon pesticide treatment. Plants with aphids had similar concentrations of terpenes as those with no aphids. Plants with aphids present had a greater diversity of compounds, though not all compounds may be terpenes. Plants with aphids differed in abundance among genotypes. Plants allocated terpenes differently between genotypes whether aphids were present or not. PSLR shows with confidence that terpenes were related to aphid abundance.

Conclusions Uroleucon nigrotuberculatum does not induce terpene production in Solidago altissima. Differences among genotypes of S. altissima in terpene concentrations supports previous findings and provides a trait difference important to herbivorous insects. Terpene allocation among genotypes of S. altissima is not related to the presence of aphids, though specific effects on aphid abundance remain unknown. PSLR shows that terpenes are related to aphid abundance in support of previous findings that found at the level of genotype these secondary metabolites are potentially important for host plant choice in this specialist aphid.

Acknowledgements ● Appalachian State University Biology Department ● Dr. Ray Williams and his graduate students ● Captain Jerry Meyers and the ASU Greenhouse ● Elizabeth White

QUESTIONS?